1. Field of the Invention
The present invention relates in general to coupled-line devices such as microwave hybrids, couplers and power dividers, especially such devices implemented using suspended-stripline technology. More particularly, the present invention relates to suspended-stripline microwave devices, and a method for manufacturing, and specifically to a suspended-stripline hybrid coupler.
2. Discussion of the Related Art
Many types of coupled line devices are known in the art, and may be manufactured using a variety of technologies. Two common technologies are microstrip and stripline. A stripline coupled-line device may include two conductive traces 25a, b, separated by a distance s and sandwiched between two dielectric substrates 26a, b, as shown in FIG. 1a. A ground plane 27a, b may usually be provided on the dielectric substrates. Microstrip coupled-line devices may include two conductive traces 25a, b disposed, spaced apart, on a dielectric substrate 26, as shown in FIG. 1b. A ground plane 27 may be disposed on an opposing side of the dielectric substrate. The coupling factor between the two conductors may depend on many factors, such as the distance s between the conductive traces 25a, b, the thickness and dielectric constant of the dielectric substrate 26, etc. The devices may be excited by an electromagnetic signal that may propagate in the conductive traces when the device is in operation. Typically, the electromagnetic signal may have a number of different modes, in particular an odd mode and an even mode. A problem that may be encountered with microstrip coupled-line devices is degrading of the coupling factor due to the unequal propagation velocities of the odd mode signal and the even mode signal in the device. One solution to this problem is to provide interdigitated xe2x80x9cteethxe2x80x9d on the inner surfaces of the coupling section, to slow down the propagation velocity of the odd mode, as shown in FIG. 2.
Another type of coupled-line device is described in U.S. Pat. Nos. 4,547,753 and 4,641,111, which are herein incorporated by reference. These devices are formed using coaxial wire technology. They include an outer conductor and first and second inner wire conductors, at least one of which has insulation bonded thereto. The two inner conductors are separated by the thickness of the insulation. The device further includes an insulating sleeve disposed in the outer conductor. In order to overcome the aforementioned problem of non-uniform propagation velocities, a low-loss, material having a dielectric constant higher than that of the sleeve is provided between the inner wire conductors and between the pair of inner conductors and the outer conductor, to slow down the even mode. However, these devices may require hand-soldering of certain contacts, and may not be suitable for use with many pick-and-place machines that are often used to automatically populate circuit boards.
Suspended-stripline is similar in structure to ordinary stripline, but instead of disposing a ground plane 27 on the dielectric substrate, as in stripline, the dielectric substrate 26 is suspended in space, usually in air, between two ground planes 27a, b, as shown in FIG. 1c. 
According to one embodiment, a suspended-stripline device comprises first and second conductive traces disposed on a dielectric substrate, each of the first and second conductive traces having a first edge and a second edge, and a housing at least partially surrounding the dielectric substrate. The device may include an input coupled to the first conductive trace, and an output coupled to at least one of the first and second conductive traces, wherein the second edge of each of the first and second conductive traces includes at least one outwardly extending protrusion.
In one example, the first and second conductive traces each include section having a predetermined length, and the at least one outwardly extending protrusion is located approximately at an end of the section. The predetermined length of the section may be, for example, approximately one quarter-wavelength corresponding to a center operating frequency of the suspended-stripline device. The size and orientation of the at least one outwardly extending protrusion may be selected so as to compensate for unequal even and odd mode propagation velocities through the suspended-stripline device.
According to another example, the section of the first conduction trace is located proximate and approximately parallel to the section of the second conductive trace. In yet another example, the second edge of at least one of the first and second conductive traces includes a plurality of outwardly extending protrusions distributed along a length of the second edge. The plurality of outwardly extending protrusions may be evenly distributed along the length of the second edge. The suspended-stripline device may have an insertion loss of less than approximately 0.2 dB.
According to another embodiment, a circuit in a suspended-stripline device comprises an input for receiving an input signal, an output for providing an output signal, a transmission line section located between the input and the output, and a lumped capacitance located at approximately one end of the transmission line section and connected between the end of the transmission line section and a reference potential. The lumped capacitance serves to compensate for differences in even and odd mode propagation velocities along the transmission line section.
In one example, the transmission line section may be approximately one quarter-wavelength long corresponding to a center operating frequency of the suspended-stripline device. The suspended-stripline device may have an insertion loss between the input and output of less than approximately 0.2 dB.
According to yet another embodiment, a suspended-stripline device comprises first and second conductive traces disposed on a dielectric substrate, and a housing at least partially surrounding the dielectric substrate. The device includes an input coupled to the first conductive trace, and an output coupled to at least one of the first and second conductive traces. An insertion loss between the input and the output is less than approximately 0.2 dB.
In one example, a dielectric constant of the dielectric substrate is in a range of approximately 2.1-3.5. In another example, each of the first and second conductive traces has a first edge and a second edge and the second edge includes at least one outwardly extending protrusion. The size and orientation of the at least one outwardly extending protrusion may be selected so as to compensate for unequal even and odd mode propagation velocities through the suspended-stripline device. According to yet another example, the first and second conductive traces each include a section having a predetermined length, and the at least one outwardly extending protrusion is located proximate an end of the section. The predetermined length of the section of the conductive traces may be approximately one quarter-wavelength corresponding to a center operating frequency of the suspended-stripline device.
According to yet another embodiment, a suspended-stripline device comprises a circuit disposed on a dielectric substrate, the circuit having an input for receiving an input signal, an output for providing an output signal, and at least one metal contact, and a metal housing at least partially surrounding the circuit, the housing including a plurality of tabs. The tabs are folded about the dielectric substrate so as to contact the at least one metal contact and electrically connected to the at least one metal contact. The height of the housing is selected so as to provide a predetermined volume of space between the dielectric substrate and a top portion of the housing.
A method of manufacturing a suspended-stripline device, according to one embodiment, comprises acts of disposing a circuit on a dielectric substrate, coating a selected piece of metal with solder, and forming a housing section out of the metal, the housing section having a predetermined shape including a plurality of tabs along an edge of the housing section. The method also includes acts of folding the plurality of tabs about an edge of the dielectric substrate and heating the housing section to a temperature sufficient to melt the solder, thereby causing the plurality of tabs to bond to a conductive trace on the dielectric substrate and securing the substrate to the housing.
According to another embodiment, a method of manufacturing a suspended-stripline device including a circuit disposed on a dielectric substrate, comprises acts of forming a metal housing section having a predetermined shape including a plurality of tabs along an edge of the housing section, and providing solder on at least one of the substrate and the plurality of tabs. The method also includes acts of folding the plurality of tabs about an edge of the dielectric substrate and heating the housing section to a temperature sufficient to melt the solder, thereby causing the plurality of tabs to bond to the substrate and secure the substrate to the housing.
In one example, the act of forming a metal housing section includes forming the housing section out of a piece of sheet metal. The act of providing solder may include coating at least a portion of the piece of sheet metal with a layer of solder.
In another example, the steps of folding and heating the tabs may be performed simultaneously, or during the same manufacturing run.
A further embodiment of a suspended-stripline device comprises first and second conductive traces disposed on a dielectric substrate, each of the first and second conductive traces having a first edge and a second edge, and a housing at least partially surrounding the dielectric substrate, a height of the housing selected so as to provide a predetermined volume of space between the dielectric substrate and the housing. The device also includes an input coupled to the first conductive trace, an output coupled to at least one of the first and second conductive traces, and means for compensating for unequal even and odd mode propagation velocities along the conductive traces.
In one example, the means for compensating may include means for reducing the even mode propagation velocity.